1. Field of the Invention
The present invention relates to a transmission structure of a working vehicle.
2. Background Art
As disclosed in U.S. Pat. No. 4,706,770, (hereinafter, “the '770 patent”) there is a well-known transmission of a working vehicle, which comprises an input shaft for inputting engine power through a continuously variable transmission (hereinafter, “CVT”), an intermediate shaft drivingly connected to the input shaft through a reversing mechanism, and an axle or axles drivingly connected to the intermediate shaft through a deceleration gear train.
As shown in FIG. 4 of the '770 patent, an intermediate shaft 100 is disposed parallel to an input shaft 98, one end thereof projecting from a transmission housing 92. For braking the vehicle, a single-plate dry disk brake 148 provided on the projecting portion of intermediate shaft 100 brakes intermediate shaft 100, thereby braking wheels 16 and 20 via axles 36, 38, 40 and 42. A gear 116 for forward traveling and a sprocket 120 for backward traveling are disposed on intermediate shaft 100. Between gear 116 and sprocket 120 is disposed a small pinion 154, which meshes with a deceleration gear 156 on a differential gear unit 157 so as to constitute the deceleration gear train. This braking structure is advantageous in that both right and left axles 36 and 38 are braked by braking only intermediate shaft 100.
However, the conventional braking structure of the '770 patent lacks durability and reliability because dry brake 148 is likely to be burnt. Converting brake 148 into a wet brake might be considered to be an easy proposition, as brake 148 is disposed in transmission housing 92 which serves as an oil sump. However, intermediate shaft 100 is desired to be disposed above axles 36 and 38 so as to ensure sufficient clearance of the vehicle. To supply sufficient oil to the brake provided on intermediate shaft 100 above axles 36 and 38, a large quantity of oil must be filled in housing 92, thereby submerging intermediate shaft 100. This submersion is undesirable as gear 116, sprocket 120 and the like stir the oil in the housing, thereby causing power loss, increase of the weight of the transmission, etc.